Although conventional lasers emitting coherent radiation at a single wavelength have become indispensable research tools, for many applications there is still a need for a laser emitting simultaneously at a plurality of predetermined wavelengths or with a predetermined spectral composition. The realization of a polychromatic or white light laser provides novel approaches in numerous fields such as medicine, spectroscopy, holography, photo-chemistry, isotope separation, spectrum analysis, optical measurement, and/or ultra-short light pulse generation. In medicine, for example, white light lasers may be used to irradiate human organs with radiation whose spectrum is optimal with respect to the absorption characteristics of the organ under treatment.
Recently, controlled spectrum generation lasers capable of emitting polychromatic or white light radiation have been developed by the inventors. See, for example, the above-identified co-pending U.S. applications; and applicants' patent applications PCT/SU 89/00163 and SU 1718313 A1. Unlike conventional lasers, controlled spectrum generation lasers emit radiation at a plurality of desired wavelengths or of a continuous spectrum with the required optical power spectral distribution.
Specifically, polychromatic or white light radiation is achieved by simultaneously pumping different portions of an active medium disposed within a suitable optical cavity or resonator. That is, the active medium is simultaneously pumped at different distances from the optical axis of the cavity, each portion of the active medium giving rise to the generation of radiation at a different desired wavelength. If the pumped portions are extended and not discrete points, the radiation comprises segments of a continuous radiation spectrum. The number of wavelength components equals the number of sites pumped, while the linewidth of each generated wavelength or bandwidth of the continuous radiation spectrum segment depends on the size of the pumped area, if the pump beam is of sufficient intensity. The operation of the controlled spectrum generation laser is disclosed in more detail in the above-identified patent applications.
Despite its breakthrough success in achieving simultaneous multi-wavelength or polychromatic lasing, the controlled spectrum generation laser has encountered new problems, some of which arise from the nature of simultaneously pumping different portions of the active medium. In this new class of lasers, it is important to be able to control the location and size of the simultaneously pumped portions of the active medium. It is also useful for the pump device mechanism to be able to control the intensity of the lasing radiation at each desired wavelength and to be able to vary temporally the generated wavelengths.
It is therefore an object of the invention to provide a device mechanism for pumping simultaneously at least two portions of the active medium of a polychromatic or white light laser.
Another object of the invention is to provide independent control for the placement of the pump radiation on the surface of the active medium.
Still another object of the invention is to provide a mechanism for controlling the size of the pump radiation.
Yet still another object of the invention is to control the intensity of the lasing radiation and to be able to vary temporally the wavelengths generated by the laser.